1. Field of the Invention
The present invention relates to a high-frequency oscillator of the microwave band or millimeter wave band, and more particularly to a high-frequency oscillator in which a high-frequency amplification device or IC (integrated circuit) chip having an amplification capability, a coplanar line of finite length, and a microstrip line are formed on both sides of a substrate.
2. Description of the Related Art
In high-frequency apparatuses or high-speed apparatuses, oscillators of the microwave band or millimeter band are extremely important functional circuits in terms of both performance and cost. In particular, when the oscillation frequency reaches high frequencies of the millimeter band, a high-output, high-quality, and low-cost oscillator has been difficult to realize due to the constraints of the high-frequency characteristics of active devices and the increase in loss in the circuit.
FIG. 1 shows one example of the configuration of a high-frequency oscillator of the prior art. In this oscillator, amplifier circuit 1 constituted by, for example, an MMIC (Microwave Monolithic Integrated Circuit) is provided on substrate 16 which is composed of, for example, a dielectric material; and feedback circuit 3 including power distribution circuit 2 is connected to the input end of amplifier circuit 17. Feedback circuit 3 is constituted as a microstrip line circuit on substrate 16. In addition, power distribution circuit 2 is electromagnetically coupled with output microstrip line 17 which is connected to the output end of amplifier circuit 1.
However, when the feedback-type circuit is constituted by a microstrip line circuit as shown in FIG. 1 and used in a high-frequency oscillator, a via-hole must be provided on the substrate for grounding the amplification circuit, and this configuration produces an inductance component which is a cause of degradation of the high-frequency characteristic of the oscillator. Further, a complicated design is required when an advanced oscillation function is to be realized, such as when injecting a frequency component which is an integral submultiple of the oscillation frequency to stabilize the oscillation frequency, i.e., when performing subharmonic injection locking; or when combining the outputs of oscillators having the same oscillation frequency to attenuate the fundamental frequency component and output only a secondary harmonic component, i.e., when implementing the so-called xe2x80x9cpushxe2x80x94pushxe2x80x9d function. The realization of these functions using the prior art configuration of an oscillator generally entailed a complex construction. Problems were encountered regarding, in particular, complexity in the design of the feedback circuit as well as the large circuit scale and size. In ultrahigh frequency bands such as the millimeter band and sub-millimeter band in particular, the design was not only complicated but also tended to be extremely difficult to fabricate.
It is an object of the present invention to provide a high-frequency oscillator which is suitable for oscillating from the microwave band to the millimeter and sub-millimeter bands, which has a simple construction, which facilitates higher oscillator output, and which easily realizes various functions with high quality.
In order to realize the above-described objects, we have succeeded in inventing a feedback-type high-frequency oscillator which has a simple constitution and which is based on a biplanar circuit technology in which a plurality of types of microwave lines are arranged on both surfaces of a substrate composed of, for example, a dielectric material.
In other words, the object of the present invention is achieved by a high-frequency oscillator which includes: a substrate; a first transmission line having a coplanar structure which is arranged on one principal surface of the substrate; an amplifier which has an input terminal and output terminal and which is inserted into the first transmission line such that the input terminal and output terminal connect to the first transmission line; and a second transmission line which is provided on the other principal surface of the substrate for electromagnetically coupling with the first transmission line and which feedback circuit with respect to the amplifier.
In the present invention, a component that is composed of, for example, a dielectric or a semiconductor may be used as the substrate. On one principal surface of the substrate, a construction such as a coplanar line or a coplanar waveguide is formed as a transmission line of coplanar structure, and on this transmission line an amplifier module or an IC (Integrated Circuit) chip having an amplifying capability is mounted as the amplifier. On the other principal surface of the substrate, a second transmission line is provided that electromagnetically couples with the transmission line that has been formed on the one principal surface of the substrate, and this second transmission line functions as a feedback circuit of the amplifier. A component of, for example, microstrip line structure may be employed as the second transmission line.
A high-frequency oscillator of this type has an amplifying device loaded on a transmission line of coplanar structure such as, for example, a coplanar line, and as a result, has the advantages of enabling easy application of flip-chip mounting by means of a surface mounting technique or a bump technique, and moreover, providing high mounting accuracy. Further, the parasitic reactance component that accompanies the amplifying device can be reduced. As a result, the previously described problems of the prior art can be greatly mitigated even when generating frequency signals of the millimeter band or sub-millimeter band, and the greater simplification, higher output, higher frequency, and moreover, high-quality characteristics of a high-frequency oscillator can thus be realized.
In addition, the high-frequency oscillator of the present invention can facilitate both the mounting of a variable-reactance element for variable control of the oscillation frequency and the injection of a subharmonic locking signal. Further, combining high-frequency oscillators of the present invention enables easy construction of a pushxe2x80x94push oscillator which generates a signal having a frequency of two times or four times the fundamental oscillation frequency.
The superior advantages of the above-described invention are the result of effectively utilizing the effects of biplanar circuit technology for constituting planar circuits on the surface of the substrate.
Further, through the application of three-dimensional monolithic microwave integrated circuit technology, the high-frequency oscillator of the present invention can be constituted as a monolithic circuit and therefore can be extremely effective in lowering the cost of a millimeter band oscillator.